Choosing A Pool Heater

by Pool Builders on 03-28-2011 in Articles

An unheated pool can only be used when the weather is suitable, so your use of your pool can be greatly increased by installing a pool heater. There are a wide range of heaters available in varying power levels, so this is not an easy decision but it is one you need to get right.

A key factor to get right is the heating capacity which must match your pool itself and your use of it. This is not as easy as you might think because although it is easy to calculate the volume of water to be heated there are other factors involved which are harder to quantify.

The "size" of pool heaters is their heating capacity which is specified in BTUs per hour. For example the Hayward H Series ranges from 150-400k but the Hayward H250 seems to be most popular. (1 BTU is the amount of energy required to raise the temperature of 1 lb of water by 1 degree Fahrenheit.) A larger heater will be a bit more efficient but it would be pointless to spend more than necessary.

The following should be considered when sizing a pool heater:

  • Pool size - The area of the pool surface and the gallons of water to be heated.
  • How you will use the pool? - Will the pool be in use all the time or intermittently (e.g. just Saturday and Sunday). If you are heating the pool intermittently then you will need a larger heater than if you are heating the pool constantly.
  • Temperature increase needed - You need to decide on your swimming season, take the coldest month and subtract the air temperature from the pool temperature you require.
  • Type of location of pool - How exposed is the pool to the wind? Being in a windy location will significantly increase the heating requirement because wind causes evaporation. You should take all practical steps to shelter the pool from the wind.
  • Do you have a pool cover? - Pools that are not covered can lose 4° F to 5° F overnight in most locations. Use of a pool cover will reduce that by about 50%.

Assuming average location factors, a general indication of the requirements for a pool heater can be calculated as follows:

Area of pool surface in square feet X Increase in temperature needed in coldest month X 12

However no formula can take into account individual location and usage factors. In general you are better off buying a slightly bigger heater than you think you need. Playing safe like this also has the advantage that the heater should be working well within its capacity and therefore should last longer.

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